Magnetic modulator



Jim 20, 1959 v R. A. HEARTz 2,870,416

MAGNETIC MODULATOR Original Filed March 26, 1953 2 Sheets-Sheet 1MILLIVOLTS .5 Abou'TPuT INVENTOR.

- ROBERT A. HEARTZ 6 5 4 3 2 l l 2 3 4 5 6 BY l I l I I I l M o c.SIGNAL MILLIVOLTS /wa ATTORNEY Jan. 20, 1959 R. A. HEAR-rz 2,870,416

MAGNETIC MODULATOR Original Filed March 26, 1953 2 Sheets-Sheet 2 HH yINVEN TOR.

ROBERT A. HEARTZ BY ATTORNEY MAGNETIC MODULATOR Continuation ofapplication Serial No. 344,698, March 26, 1953. This applicationNovember 19, 1956, Serial No. 623,008

7 claims. (ci. S32- 51) My invention relates to magnetic modulators andmore particularly to an improved magnetic modulator having superposedperpendicular magnetic fields to be hereinafter identified as a crossfield magnetic modulator. This is a continuation application of my priorapplication, Serial No. 344,698, filed March 26, 1953, on a MagneticModulator, now abandoned.

The principle of superposed perpendicular magnetic field has beenutilized previously in magnetic frequency converting devices but has notbeen applied to a modulating device in which a D. C. signal is modulatedby an alternating current supply. It is to be understood that inmodulating devices of this type that the signal voltage which isreferred to as D. C. is a signal whose frequency is low compared to thesupply frequency. The difficulty in prohibiting mutual induction betweenwindings `in devices of this type has made it non-feasible inapplication inasmuch as the outputs were subjected to extraneous signalshaving high harmo-nic components. In the subject invention, there isprovided an improved magnetic modulator which utilizes the cross fieldmagnetization principle to provide for a low input threshold or signalwith an output linear in response and stable in operation. The subjectinvention also provides a magnetic modulator of a type in which thehysteresis efiect in the magnetic core structure is substantiallyeliminated. Another object of this invention has been to provide in adevice of this type a core structure in which perpendicular magneticfields may be easily obtained. It is also an object of this invention toprovide an improved magnetic modulator utilizing a toroidal core withwindings thereon so positioned with respect to one another that mutualinduction therebetween is prohibited. it is further an object of thisinvention to provide an improved magnetic modulator having an improvedoutput carrier wave form and an A. C. output which is independent ofsignal source impedance. lt is also an object of this invention toprovide a magnetic modulator design which may be used as a voltageamplifier. These and other objects of this invention will becomeapparent from reading of the attached description together with thedrawings wherein,

Figure l is a schematic electrical circuit showing the relationship ofthe windings and the sources of power applied to and taken from thesame.

Figure 2 is a plan View of my improved cross field modulator utilizing atoroidal core and a toroidal winding,

Figure 3 is a sectional view of the cross field modulator of Figure 2taken along the lines 3 3 thereof and disclosing in section the shape ofthe toroidal core and the relative positioning of the windings of thesame,

Figure 4 is a graphdisclosing the relationship or linearity between theD. C. input signal and the A. C. modulator output signal,

l Figure 5 is a second embodiment of the invention shown in schematicform, and

tates arent O fice Figure 6 is another embodiment of the invention shownalso in schematic form.

My improved magnetic modulator is shown diagrammatically in Figure 1wherein the windings and the fields generated thereby are positionednormal to one another. However, it will be understood that a magneticcore substantially continuous in extent such as is shown in Figure 2 isassociated with the windings such that the field of one winding willalign the magnetic domains in one particular direction and the field ofthe opposite Winding which is not strong enough to re-orient theparticles or domain of the magnetic particles in the core structure willact in a direction normal thereto. In such a relationship, no magneticinduction exists between the windings on the core. ln Figure l a coil 10is designated as the alternating current field coil and adapted to beconnected at its terminals 11 to an alternating current supply. Awinding 12 is designated as the signal field winding and adapted to beconnected at its terminals i3 to a D. C. signal source. The signalsource having a frequency which is considerably lower than the supplyfrequency. Connected in parallel with the supply terminals 13 or acrosssupply terminals 13 and in parallel with winding 12 is a second pair ofterminals 15' to be designated output terminals and having connected inseries therewith a condenser 16. The magnetic structure of thismodulator is shown in its preferred form in Figure 2 in which the corestructure is a toroidal core member having an aperture 22 therein andcomprising two parts 20 and 21 which fit together in telescopic fashionand are designed to be held in assembled relationship to form the hollowtoroidal core by suitable means not shown. Positioned within theaperture 22 of the hollow toroidal core structure is the winding 1t)mounted on a spool 25. As noted above, winding 16 is the alternatingcurrent supply winding whose terminals il extend through an aperture 24in the core structure to be connected to the alternating current source.Wound around the toroidal core in the form of a toroidal winding is theD. C. signal winding 12. Although not specifically shown as such in thedrawings 2 and 3, the D. C. signal winding is sector wound on thetoroidal core so that no complete turn in the same direction as thealternating current winding 10 exists, thereby eliminating any directinductive relationship with the alternating current winding 16. Theterminals 15 and 16 are connected external of the toroidal winding andto the extremity thereof in the same manner as the D. C. source 13 isconnected thereto.

The basic premise for magnetic modulation in a device of this type isthat the A. C. supply or carrier field will saturate the entire corestructure or core volume. To this extent it will be noted that the corestructure made up of the parts 20 and 21 is tapered toward t0 its outerperiphery and reduced in cross-section at this point such 4 that themagnetic flux generated by the A. C. winding will uniformly saturate thecore structure. It will also be noted that the A. C. winding 10substantially fills the aperture 22 of the core structure to minimizethe air gap therebetween. Thus the cross-sectional area of the corestructure as seen by the A. C. supply flux is uniform over the entiresupply flux path. Although a hollow toroidal core is shown herein, itwill be understood, however, that other core configurations may beutilized in which the magnetic field may be superposed upon one anotherthe only possible limitation being the minimization of an air gapbetween the windings and the core structure and the air gap in themagnetic core structure. It will be understood, of course, that theinfluence of the magnetic fields must act perpendicular to one anotheron the core structure. lt will also be understood that the relativepositions of the A. C. and D. C. windings may be interchanged. However,to obtain the best modulated senstvity, the toroidal winding is made theD. C. signal winding and the A. C. supplywinding is positioned withinthe core structure. The toroidal core is so shaped that the area seen bythe perpendicular A. C. flux remains constant over the entire flux path.

With the arrangement of parts described above, there will be no inducedA. C. into the output winding of the device. The magnetic state of theiron in the core structure as seen from the signal winding will bedetermined by the A. C. supply field. When the A. C. supply is largeenough to saturate the core structure, the magnetic domains are lined upin a direction which is determined by the A. C. field. The perpendicularforce of the D. C. signal field is not strong enough to re-orient thesemagnetic domains. Thus the iron in the magnetic core structure as seenfrom the D. C. signal circuit reacts as an air core. When the sum of theA. C. field force and the residual field forces goes to zero, the coreas seen from the D. C. signal winding reacts as a high permeabilitymaterial. For a given D. C. signal supplied to the D. C. winding, thesignal flux will vary with the permeability of the magnetic corestructure and there will be an A. C. voltage developed across the signalwinding. ln the embodiment discussed above, this A. C. voltage will be asecond harmonic of the alternating current supply because the corestructure saturates twice during each cycle of the supply frequency. Aswill be later noted, this A. C. output can be made fundamental or of thesame frequency as the A. C. supply should the A. C. supply be biased sothat the core structure saturates only once during each cycle.

As indicated above, the shape of the magnetic core structure achievesthe uniform area as seen by the A. C. iiux path or A. C. flux therebyeliminating hysteresis eiect in the device. Further, the magnetic corestructure or the parts 20, 21 in the preferred embodiment are made of apowdered magnetic material such as a Ferrite having a high magneticpermeability. By using a powderred iron core, the shorted turn and eddycurrent effect is negligible or eliminated. Such cores are readilyfabricated by placing powdered metal in a suitable die, pressing it intoa desired shape and hardening the same. By reducing the shorted turnsand eddy currents affecting the core structures, the response time ofthe modulator is greatly improved.

Reference is made to Figure 4 showing linearity of the device orrelationship of the D. C. signal to the A. C. output of the same. Acondenser 15 is connected in series with the A. C. output terminal toeliminate the D. C. signal therefrom.

The second harmonic modulator may be converted into a fundamental outputmodulator by supplying the device with a D. C. biased A. C. supplycurrent or by supplying it with a half wave A. C. supply as shown in theembodiment of Figure 5. In this figure, it will be seen that the A. C.supply winding 10 has in series therewith a rectifier Sti which isconnected in series between the terminals 13 and winding l0. To reducethe heating effects on the core and to improve the output wave form, aresistor 3l is placed across the rectifier 3f) or in parallel therewithor a condenser 32 is connected in parallel with the A. C. supply windingl. Both the resistor and condenser may be used as indicated in thisembodiment. The A. C. supply winding l0 in this embodiment is similarlymounted in the hollow core structure in the manner shown in Figures 2and 3 and the D. C. signal winding 12 is positioned as a toroidalwinding sectionally wound on the core structure. in this embodiment thefundamental A. C. output may be taken directly from the D. C. winding inthe manner shown in connection with Figure l or aV separate transformermay he used as indicated at 35 in Figure 5 in which its primary winding36 of the transformer is connected in series with the winding i2 and theD. C. supplyterminal 7 and its secondary winding 37 is connected to theA. C. output terminals 15. A consignal.

f' Af.

denser 38 is connected in parallel with the secondary winding 37 of thetransformer 3S for filtering purposes.

ln this embodiment, with the A. C. supply source rectied or the A. C.supply signal biased, the core structure 2li, 2l will saturate only oncefor each cycle of the supply signal. Consequently the voltage generatedin the output winding 37 o-f transformer 35 which is the D. C. supplysignal of winding 12 modulated by the supply signal will have the samefrequency as the A. C.' supply.

Two cross field modulators or magnetic devices of the type describedabove may be connected so that a very large voltage gain between the D.C. signal and the A. C. output is obtained with an improved carrier waveform obtained by removing from the output the even harmonics of thecarrier and so that the A. C. output is independent of the signal sourceimpedance. In Figure 6, two cross field modulators are shown with the A.C. supply windings indicated at l@ and 10A energized from the same A. C.source 13 through ha'lf wave rectifiers 30 and SQA respectively. Thesupply windings are connected in parallel with the source 13, with therectifiers in series with each respective winding such that the windingsare energized for each half cycle of the supply signal only and with therectifier so positioned that the windings lil and 10A are energized onopposite half cycles of the supply. The D. C. windings of the respectivemodulators, indicated at l2 and l/ZA, are connected in series with oneanother to the D. C. signal source and are designed to be positioned asin the above mentioned embodiment normal to their respective A. C.winding. It will be understood that the magnetic core structures of thetwo modulators are magnetically independent of one another. In thisembodiment, the individual modulators include also a separate outputwinding indicated herein at 40 and 40A positioned on the cores ininductive relationship with the signal windings 12, ll2A and which arealso adapted to be connected in series and in opposition to one anotherbeing connected to the output terminal l5 of this apparatus. It will beunderstood that the A. C. output signal could be obtained in the mannerdisclosed in Figure l directly from the combined series connected signalwindings 12 and 12A or in the manner shown in Figure 5 from atransformerV connected in series therewith. ln this embodiment, thewindings 4t) and 40A have generated therein voltages of the fundamentalfrequency. All odd harmonics ofthe fundamental voltage subtract in theD. C. signal control circuit and add in A. C. output circuit,consequently impressing the odd harmonics on the output terminals. Evenharmonics of the generated or fundamental voltage add in the controlcircuit and subtract in the output circuit. In this embodiment, thecapacitor shown in the A. C. supply circuit of the embodiment of Figure5 may also be included to improve wave form and reduce heating affectsor a D. C. biased A. C. supply may be utilized in place of the half waverectitiers.

ln operation, this voltage ampliiier operates in the same manner as theindividual modulators described above operate. Saturation of the coredue to the A. C. supply, which in this instance is bia-sed, will takeplace only once during each cycle of the supply and the D. C. signalwill be affected by the change in permeability of the core structure toinduce in windings @il and 40A a voltage in proportion to the magnitudeof the supply As noted above, the fundamental signal and all oddharmonics add in the output circuit and consequently the output fromthis device will be of the same frequency as that of the A. C. supplysignal. Further, the fundamental and o-dd harmonics of the modulatedsignal output subtract across the D. C. signal source while the evenharmonics of the modulated signal output add across the D. C. signalsource, subtracting at theoutput circuit. This gives rise to improvedwave form of output signal and makes the modulated signal outputindependent of D. C. signal source impedance. A second harmonicamplifier or output can be obtained by eliminating the rectiers inseries with the A. C. windings or the bias in the A. C. supply clrcuitand exciting the two cores by A. C. supply currents which are 90 out ofphase.

In considering this invention it should be kept in mind that the presentdisclosure is intended to be illustrative only and that the scope of theinvention is to be determined by the appended claims.

I claim as my invention:

l. A magnetic modulator comprising, a hollow toroidal shaped core, afirst winding positioned within said hollow core and wound parallel tothe plane of the circumference of said core, ay second winding woundaround said toroidal shaped core in the form of a toroid, meansenergizing said first named winding with an alternating current supply,means energizing said second named Winding with a direct current signalsource, and means including rea eta-nce electrically coupled to saiddirect current signal source and said second named winding, said lastnamed means having a modulated direct current signal impressed on thesame.

2. A magnetic modulator comprising, a hollow toroidal shaped core ofnon-uniform cross section, a first winding positioned within said hollowcore and wound parallel to the plane of the circumference of said core,a second winding wound around said toroidal shaped core in the form of atoroid, means energizing said first named Winding with an alternatingcurrent supply, means energizing said second named winding with a directcurrent signal source, and means including a reactance electricallycoupled to said direct current signal source and said second namedwinding, said last named means having a modulated direct current signalimpressed on the same, said toroidal core being so shaped that it isuniformly saturated by said alternating current positioned therein.

3. A magnetic modulator of the cross eld type comprising, a hollowtoroidal shaped core made of a powdered magnetic material having highmagnetic permeability, a first winding positioned in said hollow coreand wound circumferencially with respect thereto, said first windingenergized from an alternating current supply, said hollow shaped corebeing so shaped in cross section that the area of the core seen by thealternating current winding is constant, a second winding wound on saidtoroidal shaped core normal to the extent or plane of said first windingand in the shape of a section of a toroid, said second winding energizedby a direct current signal, and means including a reactance electricallycoupled to said second winding, said means having an alternating signalimpressed thereon which is proportional to said direct current signalmodulated by said alternating current supply.

4. A magnetic modulator comprising, a hollow toroidal shaped core madeof a powdered magnetic material having high magnetic permeability, afirst winding positioned within said hollow core and wound parallel tothe plane of the circumference of said core, a second winding woundaround said toroidal shaped core in the form of a toroid, meansenergizing said first named winding with an alternating current supply,means energizing 6 said second named winding with a direct currentsignal source, and transformer' means having a primary winding connectedin series with said direct current signal source and said second windingand having a secondary winding adapted to have said modulated directcurrent signal induced therein, said toroidal core being so shaped thatit is uniformly saturated by the alternating current in the coilpositioned therein.

5. A magnetic modulator comprising, a hollow toroidal shaped core madeof a powdered magnetic material having high magnetic permeability, afirst winding positioned within said hollow core and wound parallel tothe plane of the circumference of said core, a second winding woundaround said toroidal shaped core in the form of a toroid, meansenergizing said first named winding with an alternating current supply,means energizing said second named winding with a direct current signalsource, third winding means electrically coupled to said second windingand having a modulated direct current signal impressed thereon, saidhollow toroidal core being so shaped that it is uniformly saturated bythe alternating current impressed on said first winding,

6. A magnetic modulator comprising, a hollow toroidal shaped core, afirst Winding positioned within said hollow core and wound parallel tothe plane of the circumference of said core, a second winding woundaround said toroidal shaped core in the form of a toroid, meansenergizing said first named winding with an alternating current supply,means electrically biasing said first named winding with the alternatingcurrent impressed thereon such that the saturation of said core takesplace in one direction only, means energizing said second named windingwith a direct current signal source, and means including a reactanceelectrically coupled to said direct current signal winding having amodulated direct current signal impressed thereon.

7. A magnetic modulator comprising, a hollow toroidal shaped core madeof a powdered magnetic material having high magnetic permeability, a rstwinding positioned within said hollow core and wound parallel to theplane of the circumference of said core, a second winding wound aroundsaid toroidal shaped core in the forrn of a toroid, means energizing oneof said windings with an alternating current supply, rectifier meansconnected to the alternating current supply and one of said windingssuch that saturation of said core takes place in one direction only,means energizing the other of said windings with a direct current signalsource, means including reactance means electrically coupled to saidother of said windings and having the modulated direct current signalimpressed thereon, said hollow toroidal core being so shaped that it isuniformly saturated by the fiux generated by said alternating current.

Wennerberg Apr. 30, 1957

